Distillation method and apparatus



Nov. 3, 1953 W. UNTERMANN ET AL DISTILLATION METHOD AND APPARATUS FiledOct. 27, 1951 ,guuuuu Patented Nov. 3, 1953 UNITED STATES PATENT OFFICEDISTILLATION METHOD AND APPARATUS corporation of Germany ApplicationOctober 27, 1951, Serial No. 253,538

16 Claims. 1

This invention relates to a new method and apparatus for thedistillation of mixtures of substances.

The separation of mixtures of substances may be efiected by continuousdistillation with the use of evaporation and rectification equipment. Inconventional evaporation and rectification equipment the rectificationcolumn receives a gaseous mixture of substances from the evaporationchamber. From this mixture one or more spe cific distillation cuts areobtained in as concentrated a form as is possible. These cuts may betaken from the column as top or side withdrawals. The sump productdischarging from the evaporator should be freed from those productswhich are to be obtained as distillates to the greatest possible extent.In most of the conventional equipment heretofore used the gaseousmixture of substances which entered the rectification column couldcontain only a, small portion of the substances which were to beobtained as distillation products. For this reason many attempts havebeen made to efiect the evaporating in the evaporation chamber in such amanner that the substances to be obtained as distillates are present inrelatively high concentrations even prior to entrance into therectification column. These attempts did not produce satisfactoryresults, however, particularly when the distillation fraction, recoveryof which was desired, was only present in a small amount in the initialproduct.

One object of this invention is to overcome the aforementioneddifiiculties.

A further object of the invention is a method and apparatus for thedistillation of mixtures of substances which will allow theconcentration of the distillation cut to be obtained, even prior toentrance into the rectifying equipment, and to free the discharging sumpproduct practically entirely from these substances. These and stillfurther objects become apparent from the following description read inconjunction with the drawing which diagrammatically shows an embodimentof an evaporation and rectifying device in accordance with theinvention.

In accordance with the invention the evaporation is carried out inmultiple consecutive stages. These stages are separated into a group offirst stages and a group of last stages. The

number of individual first stages should amount to one eighth to seveneights the entire number of stages, including all the first and laststages, and should preferably amount to about threequarters of theentire number of stages. The evaporation products from the first stagesare passed, combined with each other, to a, rectification column. Theevaporation products of the last stages are fed to a separate rectifyingor cooling device such as a separate reflux condenser.

' The reflux from the main rectifying column, i. e. the rectifyingcolumn which receives the combined evaporation products from the firststages, is advisedly returned to that individual evaporation stage inthe multiple number of first evaporation stages, having a concentrationof the substance to be recovered as said distillate thereinapproximately equal to the concentration of said substance in saidcondensate. The initial mixture from which the distillate is obtainedshould be added to the individual evaporation stage which hasapproximately the same concentration of the substance which is obtainedas a distillate as does this initial mixture. In the same manner thereflux and/or the distillate from the last stages is returned to theindividual stage or stages whose sump has most nearly the sameconcentration of the substance to be obtained as distillate as does thisreturned reflux or distillate from the last stages. Thus the freshinitial mixture which is added and the reflux or distillate from thelast stages are returned to those individual stages whose sump has aconcentration of the substance to be finally obtained as a distillatewhich most nearly equals the concentration of this substance in thereturned product.

If a separate cooler is used for the last stages, then the condensationproducts from this cooler are returned to the individual stage having acorresponding concentration of the substance to be obtained as adistillate. If the vapors from the last evaporation stage are conductedinto a separate rectifier instead of a separate cooler, the refluxand/or the head products may be conducted to the individual evaporationstages in which there is approximately the same concentration of thedesired fraction in the sump.

It has been found. advantageous to arrange all the evaporation stages inthe evaporator system annularly or consecutively in a straight line in areceptacle. It is also possible, in accordance with the invention, tohave the last evaporation stages in a second still, in which case thedirect condensate or concentrated head product may be returned to a.stage in the manner described above or the vapors may be fed to thepreceding evaporation stages.

A closed evaporation system has been found in accordance with thepresent invention in combination with a rectification column,particularly advantageous for high vacuum distillation. Such a closedsystem, however, may also be used for all pressure distillationpurposes, The closed evaporation system may have a connectedconcentration column, and only'the head product may be obtained asdistillate; It is also possible, particularly in connection withpressure distillation, to remove further fractions as side withdrawalsfrom the rectification column. Several such self-contained evaporationand rectification units may be connected in: series in or- 4 her ofindividual stages, enter the main rectification column combined witheach other. In the last stage, the concentration of the substances to berecovered as distillate is relatively low. The low concentrations mustbe substantially removed. The vapors formed by evaporation during thisremoval consist to a great extent of substances which are not to bepresent in the cut distillation product. In order not to charge therectifying column with these substances these vapors are fed separatelyto a reflux condenser or a smaller rectifying column, the vaporwithdrawal of which discharges into the vapor space of the firstevaporation stages. If a reflux condenser is usedfor the lastevaporation stages, the reflux is fed to a prior individual evaporationstage which preferably has the same concentration of the substance to berecovered as distillate. Instead of the reflux condenser, a smallrectification column may advantageously be used. The reflux from thiscolumn is fed to the first evaporation stages, while the top productenters the main rectification column in the form der to separate anydesired number of fractions 7 by distillation from an initial product.

In order to effect the distillation in accordance with the invention thestarting mixture which is to be distilled is caused to flow to one ofthe individual evaporation stages in the first evaporation stage. Thequantity of liquid from the starting mixture which is not evaporated isallowed to overflow through the subsequent individual evaporation stagesso that it will pass through all the subsequent individual stages andbe" discharged from the last individual stage of the last evaporationstage. After discharge it may be passed through further evaporation andrectification in accordance with the invention for the separation offurther fractions; from the rectification column generally constitutes amultiple of the amount of distillate which is obtained. The reflux fromthe main rectification may contain a much higher concentration of thesubstances which are to be obtained as distillate than does the initialstarting mixture. This highly concentrated reflux from the mainrectification is led to that individual evaporation stage in the firstevaporation stage having a concentration of the substance to berecovered as said distillate therein approximately equal to theconcentration of said substance in said condensate, and is partiallyevaporated. The unevaporated portion overflows to the followingsubsequent individual stages. As the substances to be recovered asdistillate are again evaporated from the reflux passed to the saidindividual stage, as it passes through the subsequent stages, a point isreached in an individual stage along the path of flow in which theconcentration of these substances is about the same as concentration inthe initial starting mixture. Fresh initial starting mixture is alwaysconducted to this stage after adjusting equilibrium in the distillationsystem. The closer this stage is to the last stages, the higher thereflux ratio. The fresh initial starting mixture is thus alwaysconducted to the stage in which the reflux has again evaporated to suchan extent that the distillate substance concentration is approximatelyequal to it. From this evaporation stage the initial starting materialand the remaining reflux flow together through the remaining individualevaporation stages until the point of discharge from the last stage. Thevapors from the first evaporation stages which are preferably equal toabout three-fourths of the 130 3841 nu of vapors combined with thevapors of the first evaporation stages. The discharging sump from thisevaporation and rectification can now automaticall'y be fedto anotheridentical system or similar system for the separation of furtherfractions. In this connection the series-com of an apparatus and whichhas flow lines. The

evaporation stages in this embodiment are shown in a row. These stagesmay also be connected in a circle without requiring any change in theflow diagram.

At I1, the material which is to be distilled enters a distributionsystem from which it can be conducted simultaneously to one or more ofthe evaporation stages, l-l-Z, which are arranged in a receptacle 13.The material is, for example, brought into' a central evaporation stage4. Due to-the overflow openings l5, all the evaporation stages arefilled up to the upper level of the overflow device 28. The evaporationof the material which is to be distilled begins advisedly by means of aheating system in each evaporation stage. The vapors from the firstevaporation stages [-9 combine in the vapor space M and enter therectifying column 23, which is filled with plates, packing or the like,in the direction shown by arrow 8, and may have any conventionalconstruction. The head or side product which is to be obtained, iswithdrawn at L! and 20 respectively. The reflux flows again to theevaporator at 2i to the first individual evaporation stage, in thedirection shown by arrow 22. The reflux, in most cases, is a multiple ofthe quantity which is to be obained as concentrated distillate. Thisreflux now displaces from evaporation stages I-4 the initial productwhich has been added at the beginning, and is again partly evaporated ineach stage so that it has, for instance, after evaporation in stage 3,

approximately the same concentration in the substances of thedistillation product, as does the initial product. From stage 4, theremaining reflux flows jointly with the starting product The units maythrough the other evaporation stages 4-I2, thus being further evaporatedin the different stages. In the same manner as over first evaporationstages l-9, there is a closed vapor space M, over last evaporationstages 9-!2 there is also such a closed vapor space 29. The evaporationchambers are separated from each other by partition I6 and the lastevaporation stages Ill-I2 evaporate the remaining quantities of thesubstances to be obtained as a distillate from the initial product. Thefinal product from stage 12, which is freed of these substances, can besubjected at 28 to further treatment, for instance in a further unitwhich is built and operated in the same or a similar manner. During theevaporating in the last evaporation stages, the liquids enter the refluxcondenser 26 combined, in the direction shown by arrow 24, and thevapors flow into the vapor space I4 through, for instance, a line 25 inthe direction shown by the arrow. The reflux 22 obtained in the refluxcondenser is fed to evaporation stage 8 so that, by this recycling, theremaining quantities of the distillate substance to be recovered areagain evaporated in concentrated form in first stages 8 and 9.

We claim:

1. Method for the distillation of mixtures of substances which comprisesestablishing a multiple number of individual series-connectedevaporation stages, including a group of first evaporation stages and agroup of last evaporation stages, said first group of evaporation stagescontaining about one eighth to seven eighths of the entire number ofindividual stages passing any uncondensed vapor from said last group ofstages to said common main rectification, subjecting such a mixture ofsubstances to evaporation in all said connected stages, subjecting thevapors evaporated from said first group of stages to a common mainrectification while separately condensing the vapors obtained from theevaporation in said last group of evaporation stages. returning thereflux from said common rectification to that individual evaporationstage having a concentration of the substance to be recovered as saiddistillate therein approximately equal to the concentration of saidsubstance in said condensate, returning the condensate from said lastgroup of stages to at least one of said first group of stages passingany uncondensed vapor from said last group of stages to said common mainrectification, and recovering at least one distillate from said commonrectificaticn.

2. Method according to claim 1, in which said condensate from said lastgroup of stages is return d to at least one of said first group ofstages having a concentration of the substance to be recovered as saiddistillate therein approximately equal to the concentration of saidsubstance in said condensate.

Method. according to claim '1, in which said first group of evaporationstages contains about three-fourths of the entire number of stages.

4. Method according to claim 1, in which a fresh quantity of such amixture of substances is added to the evaporation stage havingapproximately the same concentration of the substance recovered as saiddistillate as it has.

5. Method according to claim 1, in which said evaporation is effectedunder vacuum.

6. Method according to claim 1, in which said evaporation is effectedunder pressure.

7. Method according to claim 1, in which said condensation of the vaporsobtained from the the last individual stage and subjected to at leastone additional distillation in accordance with the method with therecovery of at least one additional distillate.

10. Apparatus for carrying out the method according to claim 1,comprising means defining a first evaporation chamber having a mainrectification column position for receiving evaporated vapors therefrom,said first evaporation chamber being subdivided into multiple individualadjacent evaporation chambers series-connected by over-flows definedtherebetween, conduit means for passing a liquid to at least one of saidindividual evaporation chambers, liquid conduct means positioned forpassing reflux from said main rectification column to at least one ofthe individual evaporation chambers defined in said first evaporationchamber, means defining a last evaporation chamber having condensingmeans positioned for receiving the vapors therefrom, said lastevaporation chamber defining multiple individual adjacent evaporationchambers seriesconnected by over-flows defined therebetween, the firstindividual chamber defined in said last evaporation chamber beingseries-connected to the last individual evaporation chamber defined bysaid first evaporation chamber, liquid conduct means positioned forremoving liquid from said last individual chamber, conduit meanspositioned for passing uncondensed vapor from said condensing means tosaid main rectification chamber, defined by said last evaporationchamber, and liquid conduct means positioned for passing condensate fromsaid condensing means to at least one of said individual chambersdefined by said first evaporation chamber.

11. Apparatus according to claim 10, in which the individual evaporationchambers'defined by said first evaporation chamber are equal in numberto about three-fourths the total number of individual evaporationchambers defined by said first and last evaporation chamber.

12. Apparatus according to claim 10, in which said first and lastevaporation chambers are defined by a partition in a main evaporationchamber, subdivided in multiple adjacent series-connected individualevaporation chambers by partial partitions defining over-flow spacestherethrough.

13. Apparatus according to claim 10, in which said individualevaporation chambers of said first and last evaporation chambers aredefined in a series-connected straight line.

14. Apparatus according to claim 10, in which the individual evaporationchambers of said first and last evaporation chamber are defined in aseries-connected circle.

15. Apparatus according to claim 10, in which said condensing meanspositioned above said last evaporation chamber is a reflux condenserhaving a conduit positioned for passing reflux therefrom to at least oneof said individual chambers defined by said first evaporation chamber,and vapor conduit means positioned for passing uncondensed vapor passingtherethrough to said first evaporation chamber.

16. Apparatus according to claim 10, in which said last evaporationchamber and condensing means therefore are defined in a subsequent,separate distillation still.

WALTER UN'IERMANN. KARL SON'DERMANN. ARTHUR MILBERS.

References Cited in the file of this patent UNITED STATES PATENTS NumberNumber Name Date McAfee Mar. 23, 1926" Wilson Feb. 21, 1933 Carney May8, 1934 Goldsbarry et a1. Dec. 11, 1951 FOREIGN PATENTS Country DateGreat Britain of 1884 Switzerland Nov. 6, 1891 France Feb. 1, 1910 GreatBritain Jan. 30, 1918,

1. METHOD FOR THE DISTILLATION OF MIXTURES OF SUBSTANCES WHICH COMPRISESESTABLISHING A MULTIPLE NUMBER OF INDIVIDUAL SERIES-CONNECTEDEVAPORATION STAGES, INCLUDING A GROUP OF FIRST EVAPORATION STAGES AND AGROUP OF LAST EVAPORATION STAGES, SAID FIRST GROUP OF EVAPORATION STAGESCONTAINING ABOUT ONE EIGHT TO SEVEN EIGHTS OF THE ENTIRE NUMBER OFINDIVIDUAL STAGES PASSING ANY UNCONDENSED VAPOR FROM SAID LAST GROUP OFSTAGES TO SAID COMMON MAIN RECTIFICATION, SUBJECTIG SUCH MIXTURE OFSUBSTANCES TO EVAPORATION IN ALL SAID CONNECTED STAGES, SUBJECTING THEVAPORS EVAPORATED FROM SAID FIRST GROUP OF STAGES TO A COMMON MAINRECYIFICATION WHILE SEPARATELY CONDENSING THE VAPORS OBTAINED FROM THEEVAPORATION IN SAID LAST GROUP OF EVAPORATION STAGES RETURNING THEREFLUX FROM SAID COMMON RECTIFICATION TO THAT INDIVIDUAL EVAPORATIONSTAGE HAVING A CONCENTRATION OF THE SUBSTANCE TO BE RECOVERED AS SAIDDISTILLATE THEREWITH APPROXIMATELY EQUAL TO THE CONCENTRATION OF SAIDSUBSTANCE IN SAID CONDENSATE, RETURNING THE CONDENSATE FROM SAID LASTGROUP OF STAGES TO AT LEAST ONE OF SAID FIRST GROUP OF STAGES PASSINGANY UNCONDENSED VAPOR FROM SAID LAST GROUP OF STAGES TO SAID COMMON MAINRECIFICATION, AND RECOVERING AT LEAST ONE DISTILLATE FROM SAID COMMONRECIFICATION.